Genes might not predict success of low-fat or low-carb diet

(Reuters Health) - People who try to avoid junk food may lose similar amounts of weight on a low-carb or low-fat diet even when their genetics suggest that one of these options should be better for them, a U.S. study found.

Researchers randomly assigned 609 obese middle-aged adults to reduce carbohydrates or fats in their diets for one year. Participants received 22 educational sessions focused on mindful eating and avoiding processed and sugary foods.

Researchers also looked to see whether participants had a particular genotype – a certain combination of the PPARG, ADRB2 and FABP2 genes – that some previous studies have linked to better results on either a low-fat or low-carb diet.

At the end of the year, people on the low-fat diet lost an average of almost 12 pounds, compared with about 13 pounds for the low-carb diet. This difference was too small to rule out the possibility that it was due to chance, and participants typically remained obese.

Weight loss also didn’t appear to be influenced by genotype, researchers report in JAMA.

“This closes the door on the possibility that the . . . genotype pattern we tested would be useful,” said lead study author Christopher Gardner of Stanford University in California.

“That does not close the door on the possibility that there are other genotype `signatures’ or patterns that could be useful,” Gardner said by email.

None of the study participants were told to cut calories. Instead of restricting carbs or fats by a prescribed amount, people were told to cut back by an amount that felt sustainable.

People were also encouraged to increase their intake of whole foods and vegetables and minimize added sugars and refined grains. To help curb mindless snacking, educators also told people to stop eating in their car or in front of their television and to make an effort to routinely dine with friends and family, shop at farmers’ markets and cook at home.

It’s possible this emphasis on healthy eating produced similar results with both diets tested in the study, said Vandana Sheth, a registered dietician and nutritionist in private practice in Los Angeles.

“Eliminating refined grains, added sugars and maximizing vegetable intake in both groups seems to suggest that steering individuals toward either a low-fat or low-carb diet is not as helpful as the diet quality,” Sheth, who wasn’t involved in the study, said by email.

Even though cutting calories wasn’t a goal for these dieters, people might still achieve this by replacing junk food with healthier alternatives, said Kevin Hall, a researcher at the National Institute of Diabetes and Digestive and Kidney Diseases who wasn’t involved in the study.

“Calorie cutting is a natural consequence of trying to decrease intake of low-quality carbs or fats in the diet,” Hall said by email.

One limitation of the study is that researchers relied on participants to accurately recall and report on what they ate and how much exercise they got.

It’s possible that the study failed to find a difference in weight loss with either diet based on genotypes at least in part because participants didn’t really follow the instructions for their assigned diet, said Susan Roberts of the USDA Nutrition Center on Aging at Tufts University in Boston.

“I would bet that if they had implemented their intervention in a way that got the participants actually adhering to the diet recommendations, they would have shown what past studies show, which is that there are individual differences in response to different diets,” Roberts, who wasn’t involved in the study, said by email.

While more research is still needed on how a person’s genotype may affect their response to certain foods or diets, the results of this study and other research still point to one proven way for people to lose weight, said Lu Qi, director of the Tulane University Obesity Research Center in New Orleans.

“There is consistent evidence that calorie restriction benefits weight loss,” Qi, who wasn’t involved in the study, said by email.